On October 18 and 19, the Chicago Architecture Foundation (CAF) will hold its fourth-annual architecture festival—Open House Chicago (OHC). Open House is a free, citywide, behind-the scenes peek at 150 of the city’s greatest buildings. In 2013, more than 55,000 individuals made 194,000 trips to the buildings included in the festival. Whether you are an architecture buff, history enthusiast or a curious urban adventurer, Open House is an annual “must-see” event.

This year’s OHC will feature buildings in 18 neighborhoods across the city. From Rogers Park to Pullman to West Town, Chicagoans and tourists will get to explore repurposed mansions, hidden rooms, sacred spaces, private clubs, iconic theatres, offices, industrial campuses, hotels and more. The most popular neighborhood in the festival annually is the Loop. And this year, CAF is proud to feature 35 Loop sites.

(Photo: 190 S LaSalle St, an OHC Loop location; Eric Allix Rogers)

Here are a few of the highlights:

The Kemper Building, One East Wacker Drive: Visit the 360-degree observation deck on the 41st floor. Closed for decades, the view from the Kemper Building has become an annual, exclusive experience for Open House Chicago visitors.

The Library at 190 S. LaSalle: This postmodern masterpiece pays homage to Burnham & Root's Masonic Temple and includes "The Library" on the 40th floor with floor-to-ceiling windows and sweeping views of the city.

The Fine Arts Building, 410 South Michigan: The Fine Arts Building was originally designed for the Studebaker Company. See the fourth-floor Venetian Court and be one of the first to step inside the Studebaker Theatre in more than a decade.

Nuveen Investments, 333 West Wacker: This dramatic green-glass tower at the fork of the Chicago River is adapted to fit an unusual triangular site. Its reflective glass mirrors the water, sky and cityscape. 333 West Wacker also happens to be Mayor Rahm Emanuel’s favorite building.

CAF is Chicago’s seventh largest cultural institution. As a nonprofit educational organization, CAF’s mission is to inspire people to discover why design matters. OHC gives people access to buildings that tell the stories of Chicago communities and cultures. By venturing into diverse neighborhoods for self-guided exploration, Open House participants come together to discover how design impacts community and place.

(Photo: Fine Arts Building)

Last year alone, Open House generated more than $5.1 million in direct spending at Chicago restaurants, shops, hotels and other businesses. None of this would be possible without the support of our partners such as the Chicago Loop Alliance and Choose Chicago. We also thank Kemper Corporation whose generous support as presenting sponsor helps keep Open House Chicago free for everyone.

So, on October 18 and 19, roll out the welcome mats at your businesses or gather your friends and participate. Either way, get ready to meet tens of thousands of Chicagoans and tourists as they take an urban trek through the Loop.